Nonionic Surfactants Promote the Incorporation of Silicone-Acrylic Hybrid Monomers in Emulsion Polymerization

The incorporation of hydrophobic and sparingly water-soluble monomers into emulsion polymer particles could lead to the development of new high-performance coatings, adhesives, personal care products, and other functional materials. Here, we show that the prototypical anionic surfactant sodium lauryl sulfate in combination with certain nonionic surfactants enables the incorporation of hydrophobic siloxane-containing monomers into conventional acrylic latex particles. This "mixed surfactant" method provides hydrophobic monomer loadings of up to 50 wt %, while undesirable macroscopic gel and the appearance of large particles due to microsuspension polymerization are held to <1 wt % (of total monomer). Fundamental experiments suggest that SLS and the secondary alcohol ethoxylate TERGITOL 15-S-9 surfactant increase monomer emulsion stability relative to other classes of nonionic surfactants examined. Increases in monomer emulsion droplet surface area and monomer solubilization/transport observed with this mixed surfactant system promote siloxane-containing monomer incorporation into growing latex particles. Our results and the guiding principles described here will jumpstart the development of polymerization processes for latex compositions that contain challenging or otherwise unusable sparingly soluble and water-insoluble monomers.